Electric resistor



July 30, 1935. R. L. HARPER ET-AL 2,009,732

' ELECTRIC RESISTOR Filed June 25, 1952 Patented July 30, 1935 UNITED STATES PATENTv OFFICE ELECTRIC RESISTOR Furnace Corporation,

ration of New York Buffalo, N. Y., a corpo- Application June 2.3, 1932, Serial No. 618,844

5 Claims.

5 invention has for its object the production of Cal an improved resistor preferably of the zig-zag type and having conducting terminals of novel construction, made in the form of a self-contained unit of comparatively small size which may be readily introduced into a seat or slot in an electrical furnace and removed therefrom without dismantling or otherwise disturbing the furnace structure.

It has been usual heretofore to emplace resistors of this general type in a chamber built into the electrical furnace with the resulting disadvantage that when replacements were required the furnace had to be partially dismantled or torn down in order to remove the resistor, necessitating shut-downs in the plant while replacements were being made. Furthermore, it has been diflcult in prior constructions adequately to protect the terminals against oxidation generally and particularly at their outer ends. Our present invention overcomes these defects by providing a unit resistor readily replaceable and having suitably protected air-cooled terminals, doing away with the need of water-cooling.

To the above and other ends which will subsequently appear our invention consists in the features and methods of construction, combinations of devices and arrangements of parts hereinafter described and particularly pointed out in the appended claims.

The preferred form of the invention is shown in the accompanying drawing wherein Fig. l is a side elevation, partly broken away, of an -electrical resistor embodying the invention;

Fig. 2 is a transverse vertical section taken on the line 2-2 in Fig. l, and

Fig. 3 is an enlarged sectional view of amodified form of terminal.

As shown in the drawing, the unit heating or resistor element designated as a whole by the unit I comprises a rectangular box or container II open at its top or one side. The box-like sheath or container may be made of any suitable refractory material that is a good conductor of heat, such as recrystallized silicon carbide or bonded silicon carbide. The container provides a housing for a resistor element proper I2,

I3 to be introduced into the container completely covering the resistor I2 on all sides. ing preferably is a mixture of fire sand or granular silicon carbide, powdered coke and a comparatively small quantity of borax or other fusible material. The packing I3 covers the resistor and fills the container up to within a short distance ofA its top, the remainder of the space above the packing being filled with a cementitious compound indicated at I4, which is made of any suitable refractory material which hardens when heated, such as silicon carbide and a binder. This cement covering I4 serves not only to provide a gas-tight covering for the open top of the container but also acts to support the conducting terminals, the ends of which are embedded in it so that when the cement hardens the terminals are held rigidly in place.

The terminals, indicated generally at I5, are of a novel construction, each comprising a graphite or carbon rod I6 enclosed in a sheath, jacket or tube I1 of porcelain, sillimanite or other refractory material, and air-tight up to at least 3000 F. The tube extends downward through the cement I4 and into the packing I3, being supported and held rigidly in place by the cement. The space between the rod and the tube is packed with an embedding material indicated at I8 which preferably is a refractory and carbonaceous mixture such as silicon carbide nes and powdered coke or graphite. This mixture minimizes the circulation of gases and insures a reducing atmosphere, the silicon carbide powder being a good conductor of heat, and is effective in cooling the larger end portion of the rod I6. At the top the tube I'I is cemented as indicated at I9 into a counter-sink 20 in a metallic gland 2|. This gland is made of a metal that is non- 'corrosive and a good conductor of electricity, such as Monel metal or nickel, so that a good electrical connection can be made with it by means of a plate or link 22 which is clamped against its top by a nut 23, said nut being screwed onto the upper reduced threaded end portion 2Ia of the gland or cap 2|.

The upper end of the terminal rod I6 is seated in a depression in the end of the gland 2|. The lower end portion of the rod is preferably reduced in diameter asl indicated at I6a and suitably contacts with the resistor I2. As a result of this construction, with the same current iiowing in the circuit more heat will be generated -in the portion I6a than in the resistor I2, making it impossible for heat to be conducted away from the resistor through the larger upper portion of This packthe rod I6. This larger portion is of such cross section that little heat is generated in it due to the passage of the electric current, so that it,

emerges from the furnace at a comparatively low temperature. The steep temperature gradient, or critical point, is confined to the point where the labrupt change in cross section of the rod occurs, namely at the shoulder between the small and large portions. The upper or large portion of the rod is covered by its refractory sheath which extends outward to the cooler point and inward or oppositely to the hotter point of smaller crosssection. At its outer end the tube or sleeve I'I makes an air-tight joint with the metallic gland 2|, due to the cement I9, and at its inner or hot end the sleeve extends into the packing I3. Due to this construction the necessity for water-cooling of the terminals is avoided, the metallic glands being non-corrosive and having a high melting point, and the large diameter of the terminal rods causing them to generate a comparatively small amount of heat.

The heating unit I is made in as small dimensions as may be without sacrificing mechanical strength, and as will be seen is of a suitable shape to enable it to be slipped into a seat or bed 2S in the wall 25 of the furnace. Although particularly adapted for ready replacement, it may of course if found desirable, be built into the furnace.

It will be noted that all of theparts comprise in our improved heating element or resistor device will withstand high temperatures. The metallic gland has a high melting point, does not corrode at high temperatures, and is not affected by carbon at high temperatures, so that no oxide is formed nor is thev composition of the metal changed, with the result that even at a very high temperature a good electrical connection is maintained. The porcelain tubes are very refractory and are air-tight up to 3000o F. or more, and are connected to the glands by a refractory joint. The terminal rods are themselves infusible and packed with a high refractory powder. As a result of the arrangement and construction, the entire unit will withstand extremely high temperatures.

Changes may. be made without departing from the invention, and as an example we have illustrated in Fig. 3 a modified form of terminal wherein the graphite rod 2B (corresponding to the rod I6 of the Figs. 1-2 construction) is made of two parts 2l and 28, the part 28 of small diameter threading into a tapped seat in the bottom of the larger part 2'I. This larger part at its upper end projects through an opening in the top of the gland 29 and is threaded as indicated at 30 to receive a block 3| of carbonaceous material with which electrical connection is directly made. The threaded portion 3D of the rod extends downward through the opening in the gland 29 which is screwed on it.

I We claim: Y

1. An electrical resistor provided with a terminal comprising a carbonaceous rod, a refractory tube of porcelain enclosing the rod and airtight` up to at least 3000 F., a' non-corrosive metallic gland of metal of high melting point into which one end of the tube is cemented to make a gas-tight joint, a refractory packing of silicon carbide nes or the like between the rod and the tube, and means providing a gas-tight joint be'- tween said resistor and the other end of the tube.

2. A heating element comprising azig-zag resistor member of carbonaceous material, an open top receptacle of silicon carbide or like refractory material in which said member is housed, a packu ing between said receptacle and said member in which said member is embedded, said packing comprising a mixture of fire sand, powdered coke and a fusible material, a cementitious covering providing a gas-tight seal over the open top of the receptacle, and conducting terminals embedded at their ends in said packing material and projecting outward from said resistor member, said terminals comprising tubular sheaths, and means providing gas-tight seals at the outer ends of said tubular sheaths.

3. A heating element comprising a zig-zag resistor member of carbonaceous material, an opentop receptacle of silicon carbide or like refractory material in which said member is housed, a packing between said receptacle and said member in which said member is* embedded, said packingA comprising a mixture of fire sand, powdered coke and a fusible material, a cementitious covering providing a gas-tight seal over the open top of the receptacle, and conducting terminals comprising carbonaceous rods and enclosing refractory tubes, the ends of said tubes being embedded in said packing.

4. A heating element comprising a carbonaceous resistance member, a container therefor of refractory material, said container having an open top, conducting terminals comprising carbonaceous rods, refractory tubes enclosing said rods, metallic glands into which the outer ends of said tubes are cemented, and a refractory packing completely covering said resistance member, and a cementitious covering providing a top for said container, 'the end portions of said tubes being embedded in said covering.

5,. A heating element comprising a carbonaceous resistance member, a container therefor of refractory material, said container having an open top, conducting terminals comprising carbonaceous rods, refractory tubes enclosing said rods, metallic glands into which the outer ends of said tubes are cemented, and a refractory packing completely covering said resistance member and a refractory cover providing a top for said container, the end portions of said tubes being cemented in said cover.

RODERICK L. HARPER. ROBERT MACDONALD, JR. 

